This invention relates to compression release brakes for internal combustion engines, and more particularly to improvements to the hydraulic circuit apparatus typically used in such brakes.
Compression release brakes for internal combustion engines are well known as shown, for example, by Cummins U.S. Pat. No. 3,220,392. In the typical compression release engine brake hydraulic circuits are provided for transferring appropriately timed motions of the engine to exhaust-valve-opening portions of the engine to cause the associated exhaust valves to open near top dead center of compression strokes of the associated engine cylinders. This hydraulic circuitry is only rendered operative when engine braking is desired and the flow of fuel to the engine is accordingly cut off. Opening the exhaust valves in this manner allows air that has been compressed in the cylinders to escape from the cylinders to the exhaust system of the engine before the engine can recover the work of compressing that air during the subsequent "power" strokes of the cylinders. The engine brake therefore temporarily converts the engine from a power source to a power-absorbing air compressor, and the engine is thereby made much more effective in slowing down a vehicle propelled by the engine. This prolongs the life of the vehicle's wheel brakes and increases the safety of operation of the vehicle.
The horsepower that an engine can absorb during compression release engine braking is strongly influenced by the timing of the exhaust valve openings relative to top dead center of the compression strokes of the associated engine cylinders. For optimum braking it is important that these exhaust valve openings be properly timed and that the exhaust valves open rapidly by an amount that is adequate to quickly release the air compressed in the associated engine cylinders. It must also be remembered that during compression release engine braking the exhaust valves must be opened against considerable resistance due to the high pressure of the air in the engine cylinders when compression release events are to be produced. All of the foregoing considerations necessitate that the engine brake hydraulic circuit associated with each engine cylinder be capable of rapidly applying a large hydraulic force to the hydraulic actuator piston that causes the exhaust valve or valves in that engine cylinder to open. The hydraulic circuit must be able to drive the actuator piston forcefully and rapidly to produce a rapid and substantial opening of the associated exhaust valve(s).
On the other hand, it may be very important to limit the stroke of the exhaust valves during compression release engine braking. This is so because during such braking the exhaust valves are opening when the top of the associated engine piston is closest to those valves (i.e., at the top dead center position). The exhaust valves must not contact the top of the associated engine piston or the engine will be damaged.
To ensure rapid and substantial but limited opening of the exhaust valves it is known to provide what is sometimes called a "clip valve" in each hydraulic circuit in a compression release engine brake. Such a clip valve allows hydraulic fluid to escape from each engine brake hydraulic circuit as soon as the actuator piston in that hydraulic circuit has travelled far enough to produce the desired maximum opening of the associated exhaust valve(s). Some examples of clip valves are shown in Hu U.S. Pat. No. 5,161,501. For example, in FIGS. 1 and 2 of the Hu patent a clip valve is shown in which a plunger 20 covers an aperture 12 in the top of slave piston 10 until the slave piston travels down beyond the limit of downward motion of the plunger established by pin 22. Aperture 12 is then uncovered, thereby allowing hydraulic fluid to escape from above slave piston 10 through the slave piston. This prevents further downward motion of the slave piston and limits the amount by which the associated engine exhaust valves are opened.
While several of the known clip valves have been highly successful, they may sometimes have certain disadvantages. For example, they tend to include a substantial number of parts, at least some of which require fairly complex machining and/or assembly. As an illustration of this the clip valve shown in FIGS. 1 and 2 of the Hu patent includes plunger 20, cross pin 22, nut 40, spring 50, and screw 70. Plunger 20 requires fairly complex machining (e.g., to produce elongated slot 28 for pin 22) and fairly complex assembly (e.g., to insert the plunger in screw 70 against the outward force of spring 50 and with the proper orientation to allow pin 22 to be passed through slot 28). There are also several possible failure modes for this apparatus. Pin 22 may come out of screw 70. Spring 50 may break. Screw 70 may break at the interface between engine brake housing 30 and nut 40 because screw 70 is weakened by being bored out for spring 50.
In view of the foregoing it is an object of this invention to provide simplified and improved clip valve apparatus for use in the hydraulic circuits of compression release brakes for internal combustion engines.
It is another object of this invention to provide compression release engine brake clip valves that have fewer parts, simpler machining, and easier assembly to lower the cost of the clip valves.
It is still another object of this invention to provide compression release engine brake clip valves that have reduced risk of breakage or failure, and which are therefore more robust and reliable in use.